In the papermaking art, an aqueous suspension containing cellulosic fibres, and optional fillers and additives, referred to as stock, is fed into a headbox which ejects the stock onto a forming wire. Water is drained from the stock through the forming wire so that a wet web of paper is formed on the wire, and the web is further dewatered and dried in the drying section of the paper machine. The obtained water, usually referred to as white water and containing fine particles such as fine fibres, fillers and additives, is usually recycled in the papermaking process. Drainage and retention aids are conventionally introduced into the stock in order to facilitate drainage and increase adsorption of fine particles onto the cellulose fibres so that they are retained with the fibres. A wide variety of drainage and retention aids are known in the art, for example anionic, non-ionic, cationic and amphoteric organic polymers, anionic and cationic inorganic materials, and many combinations thereof.
International Patent Application Publication Nos. WO 99/55964 and WO 99/55965 disclose the use of drainage and retention aids comprising cationic organic polymers having aromatic groups. The cationic organic polymers can be used alone or in combination with various anionic materials such as, for example, anionic organic and inorganic condensation polymers, e.g. sulphonated melamine-formaldehyde and silica-based particles.
It would be advantageous to be able to provide a papermaking process with improved drainage and retention. It would also be advantageous to be able to provide drainage and retention aids comprising cationic organic polymers and anionic polymers with improved drainage and retention performance.